The invention relates to an X-ray image intensifier tube, comprising an entrance window and an exit window which enclose, in conjunction with a cylindrical jacket, an evacuated space in which there are arranged an entrance screen, an exit screen, and an electron-optical imaging system.
An X-ray image intensifier tube of this kind is known from U.S. Pat. No. 4,213,055. In medical diagnostics a strong need exists for more different types of X-ray image intensifier tubes, for example, for more different dimensions of the entrance screen.
For, a long time the availability of only two entrance screen dimensions has been accepted, that is to say approximately 15 cm and approximately 25 cm. At an early stage a 25 cm tube was made suitable for imaging a 15 cm entrance screen by means of an electron-optical zoom system. More recently, the need has arisen for an X-ray image intensifier tube having a larger entrance screen, for which purpose the 35 cm tube described in U.S. Pat. No. 4,213,055 has been developed. Even though this tube also comprises an optical zoom system, that is to say for the dimensions 15, 25 and 35 cm of the entrance screen, there still is a need for, for example, a 30 cm tube and also for comparatively inexpensive tubes comprising smaller entrance screens. Specific diagnostic methods have also given rise to specific demands as regards the entrance screen and whether or not to use a fibre-optical system for the exit window, as regards the resolution of the screens, etc. This again results in specifications which cannot always be combined in a single window or screen, so that even more types of tubes are desired.
Wishes as regards electron-optical properties may also give rise to solutions which cannot be implemented in a single electrode system.
The manufacture of X-ray image intensifier tubes where each type of tube customarily treated as a separate product during the entire production process becomes less efficient as the number of types increases. It has also been found that excessive construction tolerances must be accepted in the production of notably high-quality X-ray image intensifier tubes.